Cisco said that the sample files reveal an undetected software flaw in its products

A stolen cache of files that may belong to the National Security Agency contains genuine hacking tools that not only work, but show a level of sophistication rarely seen, according to security researchers.

That includes malware that can infect a device’s firmware and can persist even if the operating system is reinstalled.

“It's terrifying because it demonstrates a serious level of expertise and technical ability,” said Brendan Dolan-Gavitt, an assistant professor at New York University’s school of engineering.